Pt atoms adsorbed onto Ge(001) surface form extremely well-ordered nanowire arrays by self-organization after high-temperature annealing. Using scanning tunneling spectroscopy/microscopy, it is shown that they are metallic and defect free. They are only 0.4 nm thick with a spacing of 1.6 nm in between, and have aspect ratios up to 1000. Their formation can be discussed in terms of a relativistic property possessed by heaviest 5d elements, and the pathway to their formation can be explained by dimer breakup on Ge(001) surface at elevated temperatures followed by a surface polymerization reaction.

The existence of one-dimensional (1D) electronic states between self-organized Pt nanowires spaced 1.6 or 2.4 nm apart on a Ge(001) surface is revealed by low-temperature scanning tunneling microscopy. These perfectly straight Pt nanowires act as barriers for a surface state (located just below the Fermi level) of the underlying terrace. The energy positions of the 1D electronic states are in good agreement with the energy levels of a quantum particle in a well. Spatial maps of the differential conductivity of the 1D electronic states conclusively reveal that these states are exclusively present in the troughs between the Pt nanowires.

Photoluminescence ͑PL͒ spectra of AgIn 5 S 8 single crystals were investigated in the 1.44-1.91 eV energy region and in the 10-170 K temperature range. The PL band was observed to be centered at 1.65 eV at 10 K and an excitation intensity of 0.97 W cm Ϫ2 . The redshift of this band with increasing temperature and with decreasing excitation intensity was observed. To explain the observed PL behavior, we propose that the emission is due to radiative recombination of a donor-acceptor pair, with an electron occupying a donor level located at 0.06 eV below the conduction band, and a hole occupying an acceptor level located at 0.32 eV above the valence band.

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The surface electronic structure of Ge(001) was studied by scanning tunneling spectroscopy. The measured surface densities of states unequivocally reveal the presence of a metallic state on the 2 1 domains, which is absent on the c4 2 domains. This metallic state, so far observed only in integral measurements, is attributed to the flip-flopping dimers that constitute the 2 1 domains. Our data also reveal a set of previously unresolved surface states, in perfect agreement with published theoretical predictions.